1. Field of the Invention
This invention relates to descent control devices, and more particularly to devices that control the descent of a person or other load supported by rope or other cable.
The descent device market is a broad market that encompasses a wide range of devices intended to control the descent of persons or objects on a vertical rope or cable. Such devices vary significantly depending on the specific intended purpose; such purposes include providing a controlled descent of an individual by another (a belay), a solo descent in a sport environment (such as rock climbing or caving), a controlled descent for tactical or rescue purposes, or an emergency egress from a building, tower or other structure. Due to the varying purposes, descent devices range from very simple (merely a carabiner or fixed “Figure 8” with a wrap of rope) to quite complex and heavy (e.g. a lever box like a Rollgliss). Sport market devices are more often light and simple, yet they require significant training to set up and use properly. Industrial versions are often very heavy and complex in order to allow the device to provide a very controlled descent with little input from the operator, including a fail safe “auto-stop” feature which automatically stops the descent if the operator is unable to operate the device (such as due to an accident or incapacity). Recently, emergency descent devices for first responders have become more prevalent, and have attempted to provide pre-rigged, simple devices that can be carried on a firefighter's person at all times in order to allow for emergency egress from buildings. While such devices have borrowed from a variety of existing devices, none has provided all of the simplicity and functionality of the proposed device.
2. Description of Prior Art
The original method of lowering oneself to the ground, a body rappel wrapping a rope around one's body, was painful on long and free-hanging drops. In the old days of fat manila rope it could be tolerated, but as thinner nylon lines came into popular use, the technique has almost disappeared from routine use. Long before the new ropes came into play, people were already looking for a better way to rappel using mechanical devices of various kinds. The basic principle of a rappel or descent device is to provide a friction surface over which a rope passes thereby slowing the descent as the person's potential energy is transferred into heat. In all cases the combination of the friction surface and the perpendicular force exerted on that surface generates the necessary total friction to slow the descent. The force exerted perpendicular to the friction surface has traditionally been provided by curving the rope around the surface and applying “back-tension” exerted on the free end of the rope by the hand of the operator. If the friction surface is limited (such as with a carabiner discussed below), the amount of tension required to be exerted on the free end of the rope can be significant (often causing significant discomfort, if not burning of the rope in ones hand). In order to provide additional friction surface to overcome this requirement, often the rope path is long and sinuous and/or the device applies extra mechanical pressure on the rope as it passes over the surface thereby increasing the friction, and hence the control over the descent. In some methods, cams act against the rope in order to apply such pressure; in other methods, pressure is applied by increasing the length of winding of the path (either by repeated wraps or by increasing the length of the device to extend the surface over which the rope passes). In many cases, the geometry of the device is variable and can be adjusted by the operator by means of a handle or lever. In some devices, the geometry is designed to “auto lock” or “auto stop” the descent when the individual releases the device (such as in an accidental fall or incapacitation).
There are many categories of modern descent devices:
Carabiners: the most basic method of controlling one's descent is by means of wrapping a rope around a carabiner or other metal ring, either singly or in combination, using a variety of hitches or other rope arrangements. The control is exerted by varying the backpressure on the rope using a free hand. Occasionally, brake bars are added to a carabiner, which aids in the control. While such devices are ubiquitous, the method requires proper configuration of a hitch (such as the Munter hitch) and continuous handling of the rope in order to properly control the descent. If the operator fails to control the free hand, the results will be an uncontrolled descent.
Figure 8's: These are fixed cast or milled devices shaped loosely like the figure “8”. As in carabiners, the rope is varyingly threaded through the device in order to provide friction. Figure 8's are small, light and relatively inexpensive, but have the same drawbacks as carabiners in that they require proper rigging and attentive handling.
Hooks and Horns: This is a broad category of fixed devices including any shaped bar or hook over and around which ropes are snaked or wrapped in order to create friction. Again, similar to Figure 8's they are light and relatively inexpensive while requiring a level of skill to operate properly.
Bobbins: Bobbins are mechanical descenders where the rope path follows an S-shaped path from bottom to top. In general the braking surface consists of two non-rotating bollards fixed to a side plate, with a second pivoting side plate provided to keep the rope from jumping off the other end of the bollards. A third (usually smaller) bollard may be provided. The attachment point for the individual usually attaches to holes in extensions of the two side plates; these holes are aligned when the side plates pivot to the closed position. Examples would be the Petzl SIMPLE or STOP (auto-stop).
Fixed Multi-bar devices: These devices consist of an arrangement whereby the rope snakes around at least three fixed bars or bollards, often machined out a single piece of metal. An example would be the Whaletail.
Moving Multi-Bar Devices: Similar to a simple bollard, the rope snakes around at least three bollards, but the geometry is such that the bollards compress against one another thereby increasing friction. The compression is controlled by a lever or screw, thereby modulating the friction. An example would be the Gemini Rescue Equipment Gemlock. These devices can be quite effective although they are often large and cumbersome.
Racks: Devices with frames that accept a number of brake bars arranged similar to a ladder, at least some of which can slide on the frame. J-frame racks have an open side; U-frame racks do not. In either case, the rope is snaked around the “rungs” causing a circuitous path and creating friction. Because the bars collapse on themselves, the inherent friction in the device can be quite high, thereby making the amount of “back tension” required to undertake a long controlled descent very manageable.
Spools: Devices where the rope wraps around a fixed drum. The drum axis can be horizontal or vertical. Friction is varied by varying the number of wraps.
Lever Boxes: Lever boxes are devices with (1) a body with a complex rope channel milled, cast, or otherwise formed into it, (2) a cover plate, and (3) a lever that allows the rappeller to control the descent, yet automatically stops the descent if the rappeller lets go (an auto-stop feature). The enclosed rope path provides some protection, although it can be a liability in heavy mud. Lever boxes tend to be complex, and the cost of manufacturing is accordingly high. They are also often large and heavy. Examples would be the Petzl Grigri, the Rollgliss and the RIT Rescue and Escape Systems F.I.R.E.-A.L.
U.S. Pat. No. 5,131,491 “Descent Controller” (Varner, 07-21-1992) is an example of a variation of a spool type descender, with an alternate ladder capstan also disclosed.
U.S. Pat. No. 5,597,052 “Descender” (Rogleja, 01-28-1997) is an example of a bobbin type descender.
U.S. Pat. No. 5,850,893 “Self-Locking Descender for a Rope with an Operating Lever” (Petzl, 12-22-1998) is another example of a bobbin type descender covering variations of the Petzl STOP device.
All of the above devices fall into either the category of simple devices that are extremely limited in their ability to control one's descent without significant training and setup time or complex devices that are either heavy, complicated to operate, expensive to manufacture or susceptible to damage and wear.